Visible light-induced 3H-indole hydrogenation using tetramethylethene as an inert hydrogen source

Nitrogen heterocycles play a crucial role in the synthesis of bioactive molecules, prompting extensive research into efficient synthetic strategies. Among these, imine hydrogenation stands out as a vital transformation, with various methodologies developed, including metal-catalyzed and Brønsted acid-catalyzed approaches. However, visible-light-induced imine hydrogenation, a relatively recent advancement, introduces unique opportunities for greener and milder reaction conditions. Herein, we report a novel approach utilizing tetramethylethene as an inert hydrogen source for the visible light-induced hydrogenation of 3H-indoles. The non-metal photocatalyst, thioxanthone-TfOH complex (9-HTXTF), demonstrated efficient catalysis under mild conditions, yielding diverse substituted indoline species.